Optical: systems and elements – Optical modulator – Light wave directional modulation
Patent
1994-12-21
1997-05-27
Ben, Loha
Optical: systems and elements
Optical modulator
Light wave directional modulation
359305, 359308, 359286, 369 54, 369116, 369 97, 369121, 356394, 356237, 250234, G02F 133
Patent
active
056337477
ABSTRACT:
An apparatus for both deflecting a beam of light illuminating a spot on a surface and varying the size of the spot, electronically, without changing any system components. The apparatus includes an acousto-optic deflector driven with a linear FM signal produced by a chirp signal generator. The linear FM signal is characterized with a dispersion rate, and the chirp signal generator includes a chirp dispersion selector to vary the dispersion rate. A beam of collimated light passes through the acousto-optic deflector and appropriate focusing optics image the beam onto a spot in a nominal focal plane. The chirp dispersion selector sets the dispersion rate in accord to a nominal rate, resulting in the beam illuminating a spot in the focal plane. Generally, the focal plane coincides with a wafer surface, of the type having periodic and non-periodic features on it. The spot size may be varied from that of a diffraction limited spot to a spot whose maximum size is system dependent. The spot size varies as a result of changing the dispersion rate of the chirp signal. The spot size may vary as it is scanned, or may remain fixed during the inspection of a wafer. In this manner, inspection by periodic feature comparison may be implemented when it proves advantageous. Alternatively, a larger spot may be obtained when periodic feature comparison would provide no benefit, and spatial filtering would achieve an enhanced signal/background.
REFERENCES:
patent: 3851951 (1974-12-01), Eveleth
patent: 4218142 (1980-08-01), Kryger et al.
patent: 4441124 (1984-04-01), Heebner et al.
patent: 4522466 (1985-06-01), Lindig et al.
patent: 4556290 (1985-12-01), Roulot
patent: 4577932 (1986-03-01), Gelbart
patent: 4601576 (1986-07-01), Galbraith
patent: 4602342 (1986-07-01), Gottlieb et al.
patent: 4614116 (1986-09-01), Huston et al.
patent: 4750163 (1988-06-01), Yamamiya et al.
patent: 4827125 (1989-05-01), Goldstein
patent: 4898471 (1990-02-01), Stonestrom et al.
patent: 4912487 (1990-03-01), Porter et al.
patent: 5008851 (1991-04-01), Brandstetter et al.
patent: 5050156 (1991-09-01), Barton
patent: 5120136 (1992-06-01), Oakley
patent: 5122898 (1992-06-01), Picault
patent: 5184343 (1993-02-01), Johann et al.
patent: 5185733 (1993-02-01), Finkelstein et al.
patent: 5210735 (1993-05-01), Hoshino et al.
Mehrdad Nikoonahad et al., "Pulse Compression Acoustic Microscopy Using SAW Filters", IEEE Transactions on Sonics and Ultrasonics, vol. SU-32, No. 2, Mar. 1985, pp. 152-163.
Ben Loha
Tencor Instruments
LandOfFree
Variable spot-size scanning apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Variable spot-size scanning apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Variable spot-size scanning apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2333144